The present invention relates generally to apparatus for working on a submerged pipeline. More particularly, the present invention concerns apparatus for providing a submerged gaseous environment in which various operations on a submerged pipeline may be performed.
During the past decade, the practical utility of submerged pipeline alignment rigs has been demonstrated by a large number of successful underwater operations. These rigs have successfully repaired damaged pipelines, added comparatively short segments of pipe to existing pipelines, connected risers of offshore platforms with a submarine pipeline, installed lateral connections to existing pipelines and the like. These various operations have been conducted at submerged depths as great as 1,000 feet.
Even though the efficacy and utility of submarine pipeline alignment rigs has been demonstrated, there are some aspects of the use and operation of known rigs which leave room for desirable improvement. For example, existing rigs are comparatively heavy and typically require specially equipped surface vessels in order to transport and service the rigs during use. Such a need for special handling equipment may necessitate delay in making the rig operational at a desired location. While ordinarily this delay does not create an insurmountable problem, there are situations in which time is of the essence and it is necessary to promptly get the rig into an operational posture. Accordingly, it is desirable to have a comparitively lightweight rig which can be transported and serviced by an available vessel of opportunity.
One aspect of the known alignment rigs which has contributed to the comparatively great weight is the use of multiple manipulators for grasping, raising and aligning the submarine conduits by the rig. While it is necessary to manipulate the pipeline in order to effect alignment between detached sections thereof, the use of a multiple manipulators on each side of a welding module can introduce extraordinary stresses in the rig and in the pipeline itself.
The known submergible alignment rigs include a unitary structure which typically has an framework truss disposed at each end to engage and manipulate a submerged pipeline. The rig must be relatively long in order to exert the necessary forces on the submerged pipeline to effect alignment of adjacent pipeline segments. With these long structures it is difficult to use the known underwater alignment rigs near an offshore tower to effect attachment between a pipeline riser and a generally horizontally extending pipeline. Moreover, when it is necessary to repair or effect a connection to an existing submerged conduit, the length of existing rigs requires an unnecessarily long section of conduit to be exposed in order to effectively use the existing rigs.
Accordingly, it will be seen that the need continues to exist for an underwater pipeline alignment which overcomes problems of the type described above.
One presently available underwater pipeline alignment rig is discussed in U.S. Pat. No. 3,641,777, issued Feb. 15, 1972 to Banjavich et al, and U.S. Pat. No. 3,785,160 issued Jan. 15, 1974 to Banjavich et al. These Banjavich et al patents are commonly assigned with the present application and disclose a working chamber that cooperates with a submersible alignment device having four manipulators each of which engages a pipeline.
Another pipeline alignment system is disclosed in U.S. Pat. No. 3,658,231, issued Apr. 25, 1972 to Gilman. The Gilman patent discloses an A-frame structure utilizing a pull-up alignment concept in which the pipeline seats against the guiderail arcuately contoured to match the pipe diameter.
A Lynch patent, U.S. Pat. No. 3,508,410 issued Apr. 28, 1970 illustrates a rigid submersible pipeline repair system having a plurality of actuators to accomodate minor pipeline bends.
A Coultrup patent, U.S. Pat. No. 3,407,611 issued Oct. 29, 1968, illustrates a submersible working chamber without pipeline manipulating apparatus.
Other pipeline connecting systems are illustrated by U.S. Pat. No. 2,500,204 issued to Roney on Mar. 14, 1950, U.S. Pat. No. 3,284,883 issued to Haverfield et al on Nov. 15, 1966 and U.S. Pat. No. 3,481,396 issued to Williams et al on Dec. 2, 1969.